I'm trying to help my dad fix his Schwinn High Timber mtn bike. It came with a 7 speed 13-28 dnp cassette. The smallest sprocket broke in half, and the teeth of the second smallest are almost completely worn (the bike is less than a year old). What cassette can I use to replace it? Any low-end name brand component will suffice. I would just like to order the correct size. I was going to order the Shimano HG50, but I noticed the lockring on the Shimano takes the Park Tool FR-5. My FR-5 does not fit the dnp cassette, does this mean they're not compatible?